High brightness, monolithic, multispectral semiconductor laser

ABSTRACT

A system and method for combining multiple emitters into a multi-wavelength output beam having a certain band and combining a plurality of these bands into a single output using non-free space combining modules.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to the following U.S. ProvisionalPatent Application, which is hereby incorporated by reference in itsentirety: U.S. Ser. No. 61/809,360 filed Apr. 6, 2013.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present embodiments relate generally to laser systems and moreparticularly to non-free space multiband laser system.

2. Description of the Prior Art

WBC methods have been developed to combine beams along a combiningdimension and produce a high power multi-wavelength output.

However, a need exists for a non-free space multi-band system that maybe combined with several multi-band beams to form a multi-broadbandlaser output.

The following application seeks to solve the problems stated.

SUMMARY OF THE INVENTION

A multi-broadband beam non-free space combiner comprising: a pluralityof beam combining modules each comprising: a plurality of externalfacets along the outside portion of a non-free space combining module,wherein at least one input facet is configured to receive a plurality ofinput optical beams; a plurality of optical modifying surfaces containedwithin the beam combining module including at least one beam convergingsurface, a diffraction surface, and a partially reflective surface,wherein beam converging surface is configured to receive the inputoptical beams and combine them substantially near the diffractionsurface, wherein the diffraction surface receives the combined beams andtransmits a multi-wavelength beam onto a partially-reflective surface,and wherein the partially-reflective receives the multi-wavelength beam,reflects a portion of the combined beams back to the diffractionsurface, and transmits the multi-wavelength beam; at least one dichroiccombiner comprising: at least two input facets configured to receivemulti-wavelength beams, wherein one of the input facets is coated tointernally reflect a first multi-wavelength beam having a firstwavelength band and transmit a second multi-wavelength beam having asecond wavelength band, wherein the first-reflected andsecond-transmitted multi-wavelengths beams are combined into a co-boresighted multi-band beam, and an output surface configured to transmitthe multi-band beam.

The multi-broadband beam non-free space combiner above, wherein the beamcombining modules and dichroic combiner are juxtaposed in a manner thatinput beams forming the multi-band beam are contained entirely in anon-free space medium.

The multi-broadband beam non-free space combiner above, wherein the beamcombining module is comprised of a material from the group consisting:solid glass, fused silica, UV-grade sapphire, CaF2, MgF2, and ZnSe.

The multi-broadband beam non-free space combiner above, furtherincluding a plurality of dichroic combiners.

The multi-broadband beam non-free space combiner above, wherein the beamcombiner module further includes an internal reflecting surface.

The multi-broadband beam non-free space combiner above, wherein theinput beams are provided by a semiconductor lasing source.

The multi-broadband beam non-free space combiner above, wherein thesemiconductor lasing is abutted next to the input facet.

The multi-broadband beam non-free space combiner of claim 1, wherein theplurality of combining modules are stacked on top of each other.

A multi-beam non-free space combiner comprising: a beam combiningmodules comprising: a plurality of external facets formed along theoutside portion of a non-free space combining module, wherein at leastone facet is configured to receive a plurality of input optical beams; aplurality of optical modifying surfaces at least partially containedwithin the beam combining module including at least one beam convergingsurface, a diffraction surface, and a partially reflective surface;wherein the beam converging surface is configured to receive the inputoptical beams and cause the beams to converge at or substantially nearthe diffraction surface, wherein the diffraction surface receives thecombined beams and transmits a multi-wavelength beam onto apartially-reflective surface, and wherein the partially-reflectivereceives the multi-wavelength beam, reflects a portion of the combinedbeams back to the diffraction surface, and transmits themulti-wavelength beam,

The multi-beam non-free space combiner above, further comprising adichroic combiner comprising abutted to the partially reflectivesurface, such that a continuous non-free space module is formed.

The multi-beam non-free space combiner above, wherein the dichroiccombiner is comprised of at least two input facets configured to receivemulti-wavelength beams, wherein one of the input facets is coated tointernally reflect a first multi-wavelength beam having a firstwavelength band and transmit a second multi-wavelength beam having asecond wavelength band, wherein the first-reflected andsecond-transmitted multi-wavelengths beams are combined into a co-boresighted multi-band beam.

A multi-beam non-free space combiner comprising: a plurality of diodebars mounted on the surface of a combining module, wherein the combiningmodule is non-free space module comprising a plurality of opticalsurfaces, wherein one of the optical surfaces is an optical lenspositioned to cause input beams from the diode bars to converge towardsa diffraction surface, wherein the diffraction surface combines theplurality of beams into a multi-wavelength beam that is transmitted ontoa partially-reflecting output coupling surface, and wherein a portion ofthe combined beams are reflected back towards the diffraction grating.

The multi-beam non-free space combiner above, further comprisingcoupling prisms mounted on the surface of the combining module toreceive the input beams from each of the diode bars and transmit saidbeams into the combining module.

The multi-beam non-free space combiner above, wherein the beam combiningmodule is comprised of a material from the group consisting: solidglass, fused silica, UV-grade sapphire, CaF2, MgF2, and ZnSe.

The multi-beam non-free space combiner above, wherein the beam combiningmodule is mounted to a cooling substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a non-free space WBC module.

FIG. 2 illustrates a plurality of non-free space WBC modules configuredto produce a multi-broad band output beam.

FIG. 3 illustrates a plurality of stacked non-free space WBC modulesconfigured to produce a multi-broad band output beam.

FIG. 4 illustrates a non-free space WBC module having multiple diode barinputs.

FIG. 5 illustrates a non-free space WBC module where the source of theinput beams is abutted against the input surface of the combiningmodule.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of this application optical elements may refer to any oflenses, mirrors, prisms and the like which redirect, reflect, bend, orin any other manner optically manipulate electromagnetic radiation.Additionally, the term beam includes visible light, infrared radiation,ultra-violet radiation, and electromagnetic radiation. Emitters includeany beam-generating device such as semiconductor elements, whichgenerate a beam, but may or may not be self-resonating. These alsoinclude fiber lasers, disk lasers, non-solid state lasers and so forth.Generally each emitter is comprised of at least one gain element. Forexample, a diode element is configured to produce a beam and has a gainelement, which may be incorporated into a resonating system.

It should also be understand that certain emitters mentioned inembodiments below, such as a diode element, may be interchanged withother types of beam emitters.

FIG. 1 shows a non-free space WBC system 100. An array of laser elements2, which could be a single diode bar, provides an input into combiningmodule 10 at an input surface that also provides a combining optic 4that is configured to cause each of the input beams to converge towardsanother optical surface 8, which has a grating formed therein. Thegrating causes the beams to combine into a multi-wavelength beam similarto other WBC systems. Here the combined multi-wavelength beam isreflected off a reflective surface 6, to help provide a compact designand then onto a partially-reflective output coupler surface 12. Aportion of the combined multi-wavelength beam is reflected back towardsthe grating 8 and back into each of the array of emitters. This resultsin stabilizing each emitter to a specific wavelength. An input surface16 of a dichroic combiner 20 receives the combined and directs ittowards a dichroic reflecting surface 14. Each dichroic reflectivesurface is configured to reflect a certain band of wavelengths whiletransmitting other bands of wavelengths. The resulting system 100produces a multi-wavelength output beam 25 that may be combined withother systems.

For example, the multi-broad beam combining system 200 of FIG. 2combines four non-free space WBC systems 100 a-d. Each system has anarray of emitters 2 a-d with accompanying gratings 8 a-d that eachproduce a unique multi-wavelength band of beams. Each of these bands isthen combined within the dichroic combiners 20 a-d to produce amulti-band output. For example, one band could be in the visible (VIS)or ultraviolet (UV) spectrum, another band could near infrared (NIR),another band could be mid infrared (MWIR), and another could be longinfrared band (LWIR). Additionally, it is contemplated a variety ofbands in between and of various bandwidths may be used.

As mentioned each combining module may have a distinct wavelengthcharacteristic to produce the desired multi-wavelength output band(beams). Wavelength beam combining can be applied to any laser with again bandwidth. For example, these lasers may include diode lasers,fiber lasers, CO2 lasers, and/or Quantum Cascade Lasers (QCLs).

Wavelength beam combining (WBC) is an incoherent process and, thus, doesnot require phasing of laser elements. In some embodiments, thebrightness of the output beam 25 scales proportionally to the totalnumber of laser elements. The output beam 25 of a WBC system is that ofa single beam. In both coherent and WBC systems, the output beam qualityis the same as that of a single emitter but the output power scales thepower from all the laser elements. If both very high spectral brightness(single frequency operation) and very high spatial brightness (singlespatial mode) is required then coherent beam combination is the onlymethod. However, in many cases single frequency operation is not desiredand may be detrimental to the functionality of the system, thus makingWBC the preferred approach.

FIG. 3 illustrates another multi-broad beam combining system 300 whereinstead of a planar combined system the combining modules 10 a-d arestacked. Similarly the array of input emitters 2 a-d may likewise bestacked and share in series or parallel power. Grating 8 a-d formed onone of the outer surfaces of combining module 10 a-d may be individuallyformed on each module as shown, or some instances formed as a singlesurface. Combining modules 10 a-d may also be initially formed as asingle unit or later stacked and combined to form a single non-freespace combining system 300. The positioning of the dichroic combiners 20a-d becomes more vertically integrated, but functions similarly to 200to produce a multi-wavelength output beam 25 having a plurality ofbands.

An alternative non-free space system 400 to that of a stacking or planarmodular combining system is illustrated in FIG. 4. Here multiple arraysof emitters 2 are mounted on the surface of a combining module 30.Coupling prisms receive the input beams and internally reflect the beamstoward an optically mounted or surface formed combing optic that causesthe beams to converge towards a grating 8, which may be a diffraction orvolume Bragg grating and combines the beams again into amulti-wavelength beam output that is transmitted onto the partiallyreflecting output coupler 12. This combining module 30 may be mounted toa cooling surface 40. System 400 may be combined with other systemssimilar to 200 or 300 using dichroic combiners to scale power and outputbands. Here it is shown that no free-space exists between the array ofemitters 2 and coupling prism 3 as the beams are directly coupled intothe system.

FIG. 5 illustrates another directly coupled system 500 having emitters 2directly coupled into combining module 10. The combining optic 4 isformed at a distance away from the input surface.

Additional optical surfaces/elements may be formed into the combiningmodules such as a chief-ray collimation optic which may help to enablethe output to be co-boresighted. A co-boresighted system is importantfor many applications such as various spectroscopy systems including:conventional absorption spectroscopy of trace chemical and biologicalagents, improvised explosive detection, differential absorption lidar(DIAL), and multi-wavelength photo-acoustic spectroscopy, materialverification, anti-counterfeiting, and threat screening.

FAC and SAC optics as well as beam rotating or repositioning surfacesmay be formed therein as well. In some embodiments the facets of thecombining module may have optical surfaces formed therein such as add areflecting layer/coating or forming a dispersive element such as gratingtherein.

Control Electronics and Software

In some embodiments, control electronics and software may be used toapply current to the individually addressable QCL array and operate theDMD chip as required for the electronic wavelength tuning. In suchembodiments, the QCLs may operate under pulsed operation, operated by apulsed QCL driver. In some embodiments, the control software may havewavelength sweep modes, ramp modes, and/or any other modes commonly usedin the art.

In at least one embodiment, coarse wavelength tuning may be accomplishedby switching the specific QCL of interest in the array. In additionalembodiments, fine wavelength tuning may be accomplished by adjusting theDMD mirror corresponding to that particular device. By adjusting the DMDmirror, electrical power may be applied to all elements of the QCL arrayconstantly, and wavelength tuning may be accomplished by adjusting theDMD mirror for feedback to a single element within the QCL array.

Although the focus of this application has been on the MID-IR range, theprinciples may apply to wavelengths outside of those ranges that aredetermined by the emitters and gratings used.

The above description is merely illustrative. Having thus describedseveral aspects of at least one embodiment of this invention includingthe preferred embodiments, it is to be appreciated that variousalterations, modifications, and improvements may readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be part of this disclosure, and are intended to bewithin the spirit and scope of the invention. Accordingly, the foregoingdescription and drawings are by way of example only.

1.-15. (canceled)
 16. A method of forming a multi-wavelength beam, themethod comprising: emitting, from a plurality of beam emitters, aplurality of input optical beams into a non-free-space medium, each beamemitter emitting at an emission wavelength; combining the plurality ofinput optical beams into a multi-wavelength beam within thenon-free-space medium; transmitting a first portion of themulti-wavelength beam out of the non-free-space medium; and reflecting asecond portion of the multi-wavelength beam, within the non-free-spacemedium, thereby causing transmission of the second portion of themulti-wavelength beam back to the plurality of beam emitters, wherebythe beam emitters are each stabilized to its emission wavelength. 17.The method of claim 16, wherein the input optical beams are combined ata diffraction surface disposed within the non-free-space medium.
 18. Themethod of claim 17, further comprising, after the input optical beamsare emitted into the non-free-space medium, converging the input opticalbeams, within the non-free-space medium, toward the diffraction surface.19. The method of claim 16, wherein the first portion of themulti-wavelength beam propagates within the non-free-space medium priorto transmission of the first portion of the multi-wavelength beam out ofthe non-free-space medium.
 20. The method of claim 19, wherein the firstportion of the multi-wavelength beam propagates within thenon-free-space medium after the second portion of the multi-wavelengthbeam is reflected.
 21. The method of claim 16, further comprisingreflecting the first portion of the multi-wavelength beam one or moretimes within the non-free-space medium before the first portion of themulti-wavelength beam is transmitted out of the non-free-space medium.22. The method of claim 16, wherein the first portion of themulti-wavelength beam is transmitted out of the non-free-space medium ata dichroic surface.
 23. The method of claim 16, further comprisingreflecting the multi-wavelength beam one or more times within thenon-free-space medium after the input optical beams are combined intothe multi-wavelength beam.
 24. The method of claim 16, wherein thenon-free-space medium comprises a combining module within which theinput optical beams are combined.
 25. The method of claim 24, wherein atleast a portion of the combining module comprises a material selectedfrom the group consisting of glass, silica, sapphire, CaF₂, MgF₂, andZnSe.
 26. The method of claim 24, wherein the non-free-space mediumcomprises a transmission module from which the first portion of themulti-wavelength beam is transmitted out of the non-free-space medium,the transmission module abutting the combining module.
 27. The method ofclaim 26, wherein at least a portion of the transmission modulecomprises a material selected from the group consisting of glass,silica, sapphire, CaF₂, MgF₂, and ZnSe.
 28. The method of claim 26,further comprising reflecting the first portion of the multi-wavelengthbeam one or more times within the transmission module prior totransmission of the first portion of the multi-wavelength beam out ofthe non-free-space medium.
 29. The method of claim 26, furthercomprising receiving one or more additional beams with the transmissionmodule and transmitting at least a portion of each additional beam outof the transmission module with the transmitted first portion of themulti-wavelength beam.
 30. The method of claim 29, wherein at least oneof the additional beams is a multi-wavelength beam.
 31. The method ofclaim 16, wherein each of the beam emitters is a diode emitter disposedwithin a diode bar.
 32. The method of claim 16, wherein at least aportion of the non-free-space medium comprises a material selected fromthe group consisting of glass, silica, sapphire, CaF₂, MgF₂, and ZnSe.33. The method of claim 16, wherein at least a portion of thenon-free-space medium is mounted on a cooling substrate.
 34. The methodof claim 16, wherein the input optical beams are combined into themulti-wavelength beam without phasing the plurality of beam emitters.35. The method of claim 16, wherein the non-free-space medium comprisesone or more coupling prisms into which the input optical beams areemitted from the plurality of beam emitters.